opengl 学习 之 05 lesson

简介

颜色和坐标一眼都是opengl 的属性，不过坐标是作为内建属性之一。

加载纹理

link

http://www.opengl-tutorial.org/uncategorized/2017/06/07/website-update/

UV

When texturing a mesh, you need a way to tell to OpenGL which part of the image has to be used for each triangle. This is done with UV coordinates.

UV坐标是用来对纹理进行适配的，以三角形的方式进行适配。

使用Blender来构建uv坐标

Linear filtering

普通的BMP映射会产生锯齿。使用Linear filtering进行滤波操作。简单来说就是颜色插值

With linear fifiltering, texture() also looks at the other texels around, and mixes the colours according to the distance to each center. This avoids the hard edges seen above.

Anisotropic fifiltering

如果你想要更好的效果，可以使用Anisotropic fifiltering(各向异性滤波)

猜测：应该是选择一个矩形方向，然后按照一定的颜色比例进行调色。

For instance, if the following texture is seen from the side, and a little bit rotated, anisotropic fifiltering will compute the colour contained in the blue rectangle by taking a fifixed number of samples (the “anisotropic level”) along its main direction.

linear and anisotropic filtering都有一个问题， If the texture is seen from far away, mixing only 4 texels won’t be enough（纹理距离足够远的话，仅仅四个像素文进行调色是远远不够的）

Mipmaps

原理很简单就是，缩放一系列纹理，然后在一定距离选择一定的纹理，然后使用linear或者anisotropic filtering

At initialisation time, you scale down your image by 2, successively, until you only have a 1x1 image (which effectively is the average of all the texels in the image)

When you draw a mesh, you select which mipmap is the more appropriate to use given how big the texel should be.

You sample this mipmap with either nearest, linear or anisotropic fifiltering

For additional quality, you can also sample two mipmaps and blend the results

use GLFW to load texture

GLuint loadTGA_glfw(const char * imagepath){
 // Create one OpenGL texture
 GLuint textureID;
 glGenTextures(1, &textureID);
 // "Bind" the newly created texture : all future texture functions will modify this texture
 glBindTexture(GL_TEXTURE_2D, textureID);
 // Read the file, call glTexImage2D with the right parameters
 glfwLoadTexture2D(imagepath, 0);
 // Nice trilinear filtering.
 glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_REPEAT);
 glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_REPEAT);
 glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
 glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR_MIPMAP_LINEAR);
 glGenerateMipmap(GL_TEXTURE_2D);
 // Return the ID of the texture we just created
 return textureID;
}

为什么要使用.DDS格式的纹理

如果直接用内存进行和GPU内存的交换会导致性能损失，如果使用DDS然后在传输的过程中进行解压，因为有专门的硬件实现硬解，所以会达到20%的性能提升。

At this point, your image is compressed in a format that is directly compatible with the GPU. Whenever calling texture() in a shader, it will uncompress it on-the-flfly. This can seem slow, but since it takes a LOT less memory, less data needs to be transferred. But memory transfers are expensive; and texture decompression is free (there is dedicated hardware for that). Typically, using texture compression yields a 20% increase in performance. So you save on performance and memory, at the expense of reduced quality.

code that load dds

GLuint loadDDS(const char * imagepath){
 unsigned char header[124];
 FILE *fp;
 /* try to open the file */
 fp = fopen(imagepath, "rb");
 if (fp == NULL)
 return 0;
 /* verify the type of file */
 char filecode[4];
 fread(filecode, 1, 4, fp);
 if (strncmp(filecode, "DDS ", 4) != 0) {
     fclose(fp);
     return 0;
 }
 /* get the surface desc */
 fread(&header, 124, 1, fp);
 unsigned int height = *(unsigned int*)&(header[8 ]);
 unsigned int width = *(unsigned int*)&(header[12]);
 unsigned int linearSize = *(unsigned int*)&(header[16]);
 unsigned int mipMapCount = *(unsigned int*)&(header[24]);
 unsigned int fourCC = *(unsigned int*)&(header[80]);
 unsigned char * buffer;
 unsigned int bufsize;
 /* how big is it going to be including all mipmaps? */
 bufsize = mipMapCount > 1 ? linearSize * 2 : linearSize;
 buffer = (unsigned char*)malloc(bufsize * sizeof(unsigned char));
 fread(buffer, 1, bufsize, fp);
 /* close the file pointer */
 fclose(fp);
 unsigned int components = (fourCC == FOURCC_DXT1) ? 3 : 4;
 unsigned int format;
 switch(fourCC)
 {
     case FOURCC_DXT1:
     format = GL_COMPRESSED_RGBA_S3TC_DXT1_EXT;
     break;
     case FOURCC_DXT3:
     format = GL_COMPRESSED_RGBA_S3TC_DXT3_EXT;
     break;
     case FOURCC_DXT5:
     format = GL_COMPRESSED_RGBA_S3TC_DXT5_EXT;
     break;
     default:
     free(buffer);
     return 0;
 }
 // Create one OpenGL texture
 GLuint textureID;
 glGenTextures(1, &textureID);
 // "Bind" the newly created texture : all future texture functions will modify this texture
 glBindTexture(GL_TEXTURE_2D, textureID);
 unsigned int blockSize = (format == GL_COMPRESSED_RGBA_S3TC_DXT1_EXT) ? 8 : 16;
 unsigned int offset = 0;
 /* load the mipmaps */
 for (unsigned int level = 0; level < mipMapCount && (width || height); ++level)
 {
 unsigned int size = ((width+3)/4)*((height+3)/4)*blockSize;
 glCompressedTexImage2D(GL_TEXTURE_2D, level, format, width, height,
 0, size, buffer + offset);
 offset += size;
 width /= 2;
 height /= 2;
 }
 free(buffer);
 return textureID;
}

TIPS

DXT压缩算法来自于DirectX，他与opengl的v坐标是相反的。需要使用( coord.u, 1.0-coord.v) ，进行UV坐标矫正。

image

DDS：感觉出现cube总出现了裂缝，不知道出了什么问题

BMP

code

// Include standard headers
#include <stdio.h>
#include <stdlib.h>

// Include GLEW
#include <GL/glew.h>

// Include GLFW
#include <GLFW/glfw3.h>
GLFWwindow* window;

// Include GLM
#include <glm/glm.hpp>
#include <glm/gtc/matrix_transform.hpp>
using namespace glm;

#include <common/shader.hpp>
#include <common/texture.hpp>

int main( void )
{
	// Initialise GLFW
	if( !glfwInit() )
	{
		fprintf( stderr, "Failed to initialize GLFW\n" );
		return -1;
	}

	glfwWindowHint(GLFW_SAMPLES, 4);
	glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 3);
	glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 3);
	glfwWindowHint(GLFW_OPENGL_FORWARD_COMPAT, GL_TRUE); // To make MacOS happy; should not be needed
	glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE);

	// Open a window and create its OpenGL context
	window = glfwCreateWindow( 1024, 768, "Tutorial 05 - Textured Cube", NULL, NULL);
	if( window == NULL ){
		fprintf( stderr, "Failed to open GLFW window. If you have an Intel GPU, they are not 3.3 compatible. Try the 2.1 version of the tutorials.\n" );
		glfwTerminate();
		return -1;
	}
	glfwMakeContextCurrent(window);

	// Initialize GLEW
	glewExperimental = true; // Needed for core profile
	if (glewInit() != GLEW_OK) {
		fprintf(stderr, "Failed to initialize GLEW\n");
		return -1;
	}

	// Ensure we can capture the escape key being pressed below
	glfwSetInputMode(window, GLFW_STICKY_KEYS, GL_TRUE);

	// Dark blue background
	glClearColor(0.0f, 0.0f, 0.4f, 0.0f);

	// Enable depth test
	glEnable(GL_DEPTH_TEST);
	// Accept fragment if it closer to the camera than the former one
	glDepthFunc(GL_LESS); 

	GLuint VertexArrayID;
	glGenVertexArrays(1, &VertexArrayID);
	glBindVertexArray(VertexArrayID);

	// Create and compile our GLSL program from the shaders
	GLuint programID = LoadShaders( "TransformVertexShader.vertexshader", "TextureFragmentShader.fragmentshader" );

	// Get a handle for our "MVP" uniform
	GLuint MatrixID = glGetUniformLocation(programID, "MVP");

	// Projection matrix : 45� Field of View, 4:3 ratio, display range : 0.1 unit <-> 100 units
	glm::mat4 Projection = glm::perspective(glm::radians(45.0f), 4.0f / 3.0f, 0.1f, 100.0f);
	// Camera matrix
	glm::mat4 View       = glm::lookAt(
								glm::vec3(4,3,3), // Camera is at (4,3,3), in World Space
								glm::vec3(0,0,0), // and looks at the origin
								glm::vec3(0,1,0)  // Head is up (set to 0,-1,0 to look upside-down)
						   );
	// Model matrix : an identity matrix (model will be at the origin)
	glm::mat4 Model      = glm::mat4(1.0f);
	// Our ModelViewProjection : multiplication of our 3 matrices
	glm::mat4 MVP        = Projection * View * Model; // Remember, matrix multiplication is the other way around

	// Load the texture using any two methods
	GLuint Texture = loadBMP_custom("uvtemplate.bmp");
	//GLuint Texture = loadDDS("uvtemplate.DDS");

	// Get a handle for our "myTextureSampler" uniform
	GLuint TextureID  = glGetUniformLocation(programID, "myTextureSampler");

	// Our vertices. Tree consecutive floats give a 3D vertex; Three consecutive vertices give a triangle.
	// A cube has 6 faces with 2 triangles each, so this makes 6*2=12 triangles, and 12*3 vertices
	static const GLfloat g_vertex_buffer_data[] = {
		-1.0f,-1.0f,-1.0f,
		-1.0f,-1.0f, 1.0f,
		-1.0f, 1.0f, 1.0f,
		 1.0f, 1.0f,-1.0f,
		-1.0f,-1.0f,-1.0f,
		-1.0f, 1.0f,-1.0f,
		 1.0f,-1.0f, 1.0f,
		-1.0f,-1.0f,-1.0f,
		 1.0f,-1.0f,-1.0f,
		 1.0f, 1.0f,-1.0f,
		 1.0f,-1.0f,-1.0f,
		-1.0f,-1.0f,-1.0f,
		-1.0f,-1.0f,-1.0f,
		-1.0f, 1.0f, 1.0f,
		-1.0f, 1.0f,-1.0f,
		 1.0f,-1.0f, 1.0f,
		-1.0f,-1.0f, 1.0f,
		-1.0f,-1.0f,-1.0f,
		-1.0f, 1.0f, 1.0f,
		-1.0f,-1.0f, 1.0f,
		 1.0f,-1.0f, 1.0f,
		 1.0f, 1.0f, 1.0f,
		 1.0f,-1.0f,-1.0f,
		 1.0f, 1.0f,-1.0f,
		 1.0f,-1.0f,-1.0f,
		 1.0f, 1.0f, 1.0f,
		 1.0f,-1.0f, 1.0f,
		 1.0f, 1.0f, 1.0f,
		 1.0f, 1.0f,-1.0f,
		-1.0f, 1.0f,-1.0f,
		 1.0f, 1.0f, 1.0f,
		-1.0f, 1.0f,-1.0f,
		-1.0f, 1.0f, 1.0f,
		 1.0f, 1.0f, 1.0f,
		-1.0f, 1.0f, 1.0f,
		 1.0f,-1.0f, 1.0f
	};

	// Two UV coordinatesfor each vertex. They were created with Blender.
	static const GLfloat g_uv_buffer_data[] = {
		0.000059f, 1.0f-0.000004f,
		0.000103f, 1.0f-0.336048f,
		0.335973f, 1.0f-0.335903f,
		1.000023f, 1.0f-0.000013f,
		0.667979f, 1.0f-0.335851f,
		0.999958f, 1.0f-0.336064f,
		0.667979f, 1.0f-0.335851f,
		0.336024f, 1.0f-0.671877f,
		0.667969f, 1.0f-0.671889f,
		1.000023f, 1.0f-0.000013f,
		0.668104f, 1.0f-0.000013f,
		0.667979f, 1.0f-0.335851f,
		0.000059f, 1.0f-0.000004f,
		0.335973f, 1.0f-0.335903f,
		0.336098f, 1.0f-0.000071f,
		0.667979f, 1.0f-0.335851f,
		0.335973f, 1.0f-0.335903f,
		0.336024f, 1.0f-0.671877f,
		1.000004f, 1.0f-0.671847f,
		0.999958f, 1.0f-0.336064f,
		0.667979f, 1.0f-0.335851f,
		0.668104f, 1.0f-0.000013f,
		0.335973f, 1.0f-0.335903f,
		0.667979f, 1.0f-0.335851f,
		0.335973f, 1.0f-0.335903f,
		0.668104f, 1.0f-0.000013f,
		0.336098f, 1.0f-0.000071f,
		0.000103f, 1.0f-0.336048f,
		0.000004f, 1.0f-0.671870f,
		0.336024f, 1.0f-0.671877f,
		0.000103f, 1.0f-0.336048f,
		0.336024f, 1.0f-0.671877f,
		0.335973f, 1.0f-0.335903f,
		0.667969f, 1.0f-0.671889f,
		1.000004f, 1.0f-0.671847f,
		0.667979f, 1.0f-0.335851f
	};

	GLuint vertexbuffer;
	glGenBuffers(1, &vertexbuffer);
	glBindBuffer(GL_ARRAY_BUFFER, vertexbuffer);
	glBufferData(GL_ARRAY_BUFFER, sizeof(g_vertex_buffer_data), g_vertex_buffer_data, GL_STATIC_DRAW);

	GLuint uvbuffer;
	glGenBuffers(1, &uvbuffer);
	glBindBuffer(GL_ARRAY_BUFFER, uvbuffer);
	glBufferData(GL_ARRAY_BUFFER, sizeof(g_uv_buffer_data), g_uv_buffer_data, GL_STATIC_DRAW);

	do{

		// Clear the screen
		glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

		// Use our shader
		glUseProgram(programID);

		// Send our transformation to the currently bound shader,
		// in the "MVP" uniform
		glUniformMatrix4fv(MatrixID, 1, GL_FALSE, &MVP[0][0]);

		// Bind our texture in Texture Unit 0
		glActiveTexture(GL_TEXTURE0);
		glBindTexture(GL_TEXTURE_2D, Texture);
		// Set our "myTextureSampler" sampler to use Texture Unit 0
		glUniform1i(TextureID, 0);

		// 1rst attribute buffer : vertices
		glEnableVertexAttribArray(0);
		glBindBuffer(GL_ARRAY_BUFFER, vertexbuffer);
		glVertexAttribPointer(
			0,                  // attribute. No particular reason for 0, but must match the layout in the shader.
			3,                  // size
			GL_FLOAT,           // type
			GL_FALSE,           // normalized?
			0,                  // stride
			(void*)0            // array buffer offset
		);

		// 2nd attribute buffer : UVs
		glEnableVertexAttribArray(1);
		glBindBuffer(GL_ARRAY_BUFFER, uvbuffer);
		glVertexAttribPointer(
			1,                                // attribute. No particular reason for 1, but must match the layout in the shader.
			2,                                // size : U+V => 2
			GL_FLOAT,                         // type
			GL_FALSE,                         // normalized?
			0,                                // stride
			(void*)0                          // array buffer offset
		);

		// Draw the triangle !
		glDrawArrays(GL_TRIANGLES, 0, 12*3); // 12*3 indices starting at 0 -> 12 triangles

		glDisableVertexAttribArray(0);
		glDisableVertexAttribArray(1);

		// Swap buffers
		glfwSwapBuffers(window);
		glfwPollEvents();

	} // Check if the ESC key was pressed or the window was closed
	while( glfwGetKey(window, GLFW_KEY_ESCAPE ) != GLFW_PRESS &&
		   glfwWindowShouldClose(window) == 0 );

	// Cleanup VBO and shader
	glDeleteBuffers(1, &vertexbuffer);
	glDeleteBuffers(1, &uvbuffer);
	glDeleteProgram(programID);
	glDeleteTextures(1, &Texture);
	glDeleteVertexArrays(1, &VertexArrayID);

	// Close OpenGL window and terminate GLFW
	glfwTerminate();

	return 0;
}

#ifndef TEXTURE_HPP
#define TEXTURE_HPP

// Load a .BMP file using our custom loader
GLuint loadBMP_custom(const char * imagepath);

//// Since GLFW 3, glfwLoadTexture2D() has been removed. You have to use another texture loading library,
//// or do it yourself (just like loadBMP_custom and loadDDS)
//// Load a .TGA file using GLFW's own loader
//GLuint loadTGA_glfw(const char * imagepath);

// Load a .DDS file using GLFW's own loader
GLuint loadDDS(const char * imagepath);

#endif

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#include <GL/glew.h>

#include <GLFW/glfw3.h>

GLuint loadBMP_custom(const char * imagepath){

	printf("Reading image %s\n", imagepath);

	// Data read from the header of the BMP file
	unsigned char header[54];
	unsigned int dataPos;
	unsigned int imageSize;
	unsigned int width, height;
	// Actual RGB data
	unsigned char * data;

	// Open the file
	FILE * file = fopen(imagepath,"rb");
	if (!file){
		printf("%s could not be opened. Are you in the right directory ? Don't forget to read the FAQ !\n", imagepath);
		getchar();
		return 0;
	}

	// Read the header, i.e. the 54 first bytes

	// If less than 54 bytes are read, problem
	if ( fread(header, 1, 54, file)!=54 ){
		printf("Not a correct BMP file\n");
		fclose(file);
		return 0;
	}
	// A BMP files always begins with "BM"
	if ( header[0]!='B' || header[1]!='M' ){
		printf("Not a correct BMP file\n");
		fclose(file);
		return 0;
	}
	// Make sure this is a 24bpp file
	if ( *(int*)&(header[0x1E])!=0  )         {printf("Not a correct BMP file\n");    fclose(file); return 0;}
	if ( *(int*)&(header[0x1C])!=24 )         {printf("Not a correct BMP file\n");    fclose(file); return 0;}

	// Read the information about the image
	dataPos    = *(int*)&(header[0x0A]);
	imageSize  = *(int*)&(header[0x22]);
	width      = *(int*)&(header[0x12]);
	height     = *(int*)&(header[0x16]);

	// Some BMP files are misformatted, guess missing information
	if (imageSize==0)    imageSize=width*height*3; // 3 : one byte for each Red, Green and Blue component
	if (dataPos==0)      dataPos=54; // The BMP header is done that way

	// Create a buffer
	data = new unsigned char [imageSize];

	// Read the actual data from the file into the buffer
	fread(data,1,imageSize,file);

	// Everything is in memory now, the file can be closed.
	fclose (file);

	// Create one OpenGL texture
	GLuint textureID;
	glGenTextures(1, &textureID);

	// "Bind" the newly created texture : all future texture functions will modify this texture
	glBindTexture(GL_TEXTURE_2D, textureID);

	// Give the image to OpenGL
	glTexImage2D(GL_TEXTURE_2D, 0,GL_RGB, width, height, 0, GL_BGR, GL_UNSIGNED_BYTE, data);

	// OpenGL has now copied the data. Free our own version
	delete [] data;

	// Poor filtering, or ...
	//glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
	//glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST); 

	// ... nice trilinear filtering ...
	glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_REPEAT);
	glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_REPEAT);
	glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
	glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR_MIPMAP_LINEAR);
	// ... which requires mipmaps. Generate them automatically.
	glGenerateMipmap(GL_TEXTURE_2D);

	// Return the ID of the texture we just created
	return textureID;
}

// Since GLFW 3, glfwLoadTexture2D() has been removed. You have to use another texture loading library,
// or do it yourself (just like loadBMP_custom and loadDDS)
//GLuint loadTGA_glfw(const char * imagepath){
//
//	// Create one OpenGL texture
//	GLuint textureID;
//	glGenTextures(1, &textureID);
//
//	// "Bind" the newly created texture : all future texture functions will modify this texture
//	glBindTexture(GL_TEXTURE_2D, textureID);
//
//	// Read the file, call glTexImage2D with the right parameters
//	glfwLoadTexture2D(imagepath, 0);
//
//	// Nice trilinear filtering.
//	glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_REPEAT);
//	glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_REPEAT);
//	glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
//	glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR_MIPMAP_LINEAR);
//	glGenerateMipmap(GL_TEXTURE_2D);
//
//	// Return the ID of the texture we just created
//	return textureID;
//}

#define FOURCC_DXT1 0x31545844 // Equivalent to "DXT1" in ASCII
#define FOURCC_DXT3 0x33545844 // Equivalent to "DXT3" in ASCII
#define FOURCC_DXT5 0x35545844 // Equivalent to "DXT5" in ASCII

GLuint loadDDS(const char * imagepath){

	unsigned char header[124];

	FILE *fp; 

	/* try to open the file */
	fp = fopen(imagepath, "rb");
	if (fp == NULL){
		printf("%s could not be opened. Are you in the right directory ? Don't forget to read the FAQ !\n", imagepath); getchar();
		return 0;
	}

	/* verify the type of file */
	char filecode[4];
	fread(filecode, 1, 4, fp);
	if (strncmp(filecode, "DDS ", 4) != 0) {
		fclose(fp);
		return 0;
	}

	/* get the surface desc */
	fread(&header, 124, 1, fp); 

	unsigned int height      = *(unsigned int*)&(header[8 ]);
	unsigned int width	     = *(unsigned int*)&(header[12]);
	unsigned int linearSize	 = *(unsigned int*)&(header[16]);
	unsigned int mipMapCount = *(unsigned int*)&(header[24]);
	unsigned int fourCC      = *(unsigned int*)&(header[80]);

	unsigned char * buffer;
	unsigned int bufsize;
	/* how big is it going to be including all mipmaps? */
	bufsize = mipMapCount > 1 ? linearSize * 2 : linearSize;
	buffer = (unsigned char*)malloc(bufsize * sizeof(unsigned char));
	fread(buffer, 1, bufsize, fp);
	/* close the file pointer */
	fclose(fp);

	unsigned int components  = (fourCC == FOURCC_DXT1) ? 3 : 4;
	unsigned int format;
	switch(fourCC)
	{
	case FOURCC_DXT1:
		format = GL_COMPRESSED_RGBA_S3TC_DXT1_EXT;
		break;
	case FOURCC_DXT3:
		format = GL_COMPRESSED_RGBA_S3TC_DXT3_EXT;
		break;
	case FOURCC_DXT5:
		format = GL_COMPRESSED_RGBA_S3TC_DXT5_EXT;
		break;
	default:
		free(buffer);
		return 0;
	}

	// Create one OpenGL texture
	GLuint textureID;
	glGenTextures(1, &textureID);

	// "Bind" the newly created texture : all future texture functions will modify this texture
	glBindTexture(GL_TEXTURE_2D, textureID);
	glPixelStorei(GL_UNPACK_ALIGNMENT,1);	

	unsigned int blockSize = (format == GL_COMPRESSED_RGBA_S3TC_DXT1_EXT) ? 8 : 16;
	unsigned int offset = 0;

	/* load the mipmaps */
	for (unsigned int level = 0; level < mipMapCount && (width || height); ++level)
	{
		unsigned int size = ((width+3)/4)*((height+3)/4)*blockSize;
		glCompressedTexImage2D(GL_TEXTURE_2D, level, format, width, height,
			0, size, buffer + offset); 

		offset += size;
		width  /= 2;
		height /= 2; 

		// Deal with Non-Power-Of-Two textures. This code is not included in the webpage to reduce clutter.
		if(width < 1) width = 1;
		if(height < 1) height = 1;

	} 

	free(buffer); 

	return textureID;

}

#version 330 core

// Input vertex data, different for all executions of this shader.
layout(location = 0) in vec3 vertexPosition_modelspace;
layout(location = 1) in vec2 vertexUV;

// Output data ; will be interpolated for each fragment.
out vec2 UV;

// Values that stay constant for the whole mesh.
uniform mat4 MVP;

void main(){

	// Output position of the vertex, in clip space : MVP * position
	gl_Position =  MVP * vec4(vertexPosition_modelspace,1);

	// UV of the vertex. No special space for this one.
	UV = vertexUV;
}

#version 330 core

// Interpolated values from the vertex shaders
in vec2 UV;

// Ouput data
out vec3 color;

// Values that stay constant for the whole mesh.
uniform sampler2D myTextureSampler;

void main(){

	// Output color = color of the texture at the specified UV
	color = texture( myTextureSampler, UV ).rgb;
}